1. Field of the Invention
The present invention is directed in general to the field of semiconductor fabrication and integrated circuits. In one aspect, the present invention relates to complementary metal oxide semiconductor (CMOS) field effect transistors (FETs) fabricated with strained semiconductor channel regions
2. Description of the Related Art
CMOS devices, such as NMOS or PMOS transistors, have conventionally been fabricated on semiconductor wafers with NMOS and PMOS having same channel material characteristics. While it is possible to improve carrier mobility by intentionally stressing the channels of NMOS and/or PMOS transistors, it is difficult to simultaneously improve the carrier mobility for both types of devices formed on a uniformly-strained substrate because PMOS carrier mobility and NMOS carrier mobility are optimized under different types of stress. For example, those skilled in the art have discovered that electron mobility for NMOS devices having <110> channel oriented channels may be improved by intentionally implementing a tensile stress in NMOS transistor channels to improve carrier mobility, but <110> PMOS devices require a compressive channel stress for performance boosting. Moreover, stress conditions that optimize carrier mobility may negatively impact other device characteristics such as threshold voltage, thereby complicating the selection of stress conditions.
Accordingly, there is a need for improved semiconductor processes and devices to overcome the problems in the art, such as outlined above. Further limitations and disadvantages of conventional processes and technologies will become apparent to one of skill in the art after reviewing the remainder of the present application with reference to the drawings and detailed description which follow.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the drawings have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for purposes of promoting and improving clarity and understanding. Further, where considered appropriate, reference numerals have been repeated among the drawings to represent corresponding or analogous elements.